The present invention relates to a no-load-run strap release control mechanism for a strapping machine which uses a brake mechanism to stop the welding mechanism from operating during the release of a no-load-run strap.
Regular strapping machines commonly use polypropylene straps to tie up things. When a strapping machine is used, a no-load-run will occur when the control switch is triggered by an error. FIG. 1 shows a no-load-run strap release control mechanism according to the prior art, which comprises a rotary table 61 with a cut 611 securely fixed to the return wheel 6, and a proximity detector 62 disposed adjacent to the rotary table 61. When the strap is stretched during the binding process, the revolving speed of the rotary table 61 is reduced, and the proximity detector 62 is induced to send a signal to the control circuit, so that the control circuit drives the cutting and welding mechanism of the strapping machine to cut and seal the strap. If a no-load-run occurs, the proximity detector 62 detects no signal, and the cam (not shown) of the strapping machine will trigger a limit switch, causing the cam reversed after cutting off the strap and before the proceeding of the welding process, permitting the looped strap section to trip off by means of its resilient material property. Because the cam must be forced to rotate in the reversed direction upon the occurence of a no-load-run, a reversible motor must be installed to turn the cam. Furthermore, a same mechanism must be installed in the forward wheel 63 of the strapping machine. As dust tends to occur during the strapping procedure, the proximity detectors 62 will be covered with dust easily, causing detecting errors.